Handbook of Information Security Management
(Publisher: CRC Press LLC)
Author(s): Hal Tipton and Micki Krause, Consulting Editors
ISBN: 0849399475
Publication Date: 01/01/98

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User Access Authorities

Resource protection mechanisms may be either manual or automatic. The size of the installation must be evaluated when the security administrator is considering the use of a manual methodology because it can quickly be outgrown, becoming impossible to control and maintain. Automatic mechanisms are typically more costly to implement but may soon recoup their cost in productivity savings.

Regardless of the automation level of a particular mechanism, it is necessary to be able to separate types of access according to user needs. The most effective approach is one of least privilege; that is, users should not be allowed to undertake actions beyond what their specific job responsibilities warrant. With this method, it is useful to divide users into several groups. Each group is then assigned the most restrictive authority available while permitting users to carry out the functions of their jobs.

There are several options to which users may be assigned. The most restrictive authority and the one to which most users should be assigned is read only. Users assigned to read only are allowed to view data but are not allowed to add, delete, or make changes.

The next level is read/write access, which allows users to add or modify data within applications for which they have authority. This level permits individuals to access a particular application and read, add, and write over data in files copied from the original location.

A third access level is change. This option permits the holder not only to read a file and write data to another file location but to change the original data, thereby altering it permanently.

When analyzing user access authorities, the security practitioner must distinguish between access to discretionary information resources (which is regulated only by personal judgment) and access to nondiscretionary resources (which is strictly regulated on the basis of the predetermined transaction methodology). Discretionary user access is defined as the ability to manipulate data by using custom-developed programs or a general-purpose utility program. The only information logged for discretionary access in an information security control mechanism is the type of data accessed and at what level of authority. It is not possible to identify specific uses of the data.

Nondiscretionary user access, on the other hand, is performed while executing specific business transactions that affect information in a predefined way. For this type of access, users can perform only certain functions in carefully structured ways. For example, in a large accounting system, many people prepare transactions that affect the ledger. Typically, one group of accounting analysts is able to enter the original source data but not to review or access the overall results. Another group has access to the data for review but is not able to alter the results. In addition, with nondiscretionary access, the broad privileges assigned to a user for working with the system itself should be analyzed in conjunction with the user’s existing authority to execute the specific transactions needed for the current job assignment. This type of access is important when a user can be authorized to both read and add information but not to delete or change it. For example, bank tellers need access to customer account information to add deposits but do not need the ability to change any existing information.

At times, even nondiscretionary access may not provide sufficient control. In such situations, special access controls can be invoked. Additional restrictions may be implemented in various combinations of add, change, delete, and read capabilities. The control and auditability requirements that have been designed into each application are used to control the management of the information assets involved in the process.

Special Classifications

A growing trend is to give users access to only resource subsets or perhaps to give them the ability to update information only when performing a specific task and following a specific procedure. This has created the need for a different type of access control in which authorization can be granted on the basis of both the individual requesting resource access and the intended use of that resource. This type of control can be exercised by the base access control mechanism (i.e., the authorization list, including user ID and program combinations).

Another method sometimes used provides the required access authority along with the programs the user has authorization for; this information is provided only after the individual’s authority has been verified by an authorization program. This program may incorporate additional constraints (e.g., scoped access control) and may include thorough access logging along with ensuring data integrity when updating information.

Scoped access control is necessary when users need access only to selected areas or records within a resource, thereby controlling the access granted to a small group on the basis of an established method for separating that group from the rest of the data. In general, the base access control mechanism is activated at the time of resource initialization (i.e., when a data set is prepared for access). Therefore, scoped access control should be provided by the data base management system or the application program. For example, in personnel systems, managers are given authority to access only the information related to their employees.

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